In the conventional quality determination of the Heart & Cupid optical effects of the diamond, a gemologist has determined the quality of a gem in sensory terms according to a unique criterion for determination on the basis of eight heart images and eight cupid images taken by a CCD camera.
Moreover, as another conventional technique, there is a technique described in Patent Document 1.
The technique is a gem appraising device including: a gem illumination unit, having an illuminated space in which a gem to be appraised is arranged, which illuminates a gem arranged in the illuminated space; holding means which holds the gem in such a way that the posture of the gem is variable in the illuminated space of the gem illumination unit; a light source which generates light impinging on the illuminated space of the gem illumination unit; an enlarging optical system which takes in a reflected light of the gem illuminated in the gem illumination unit and forms an enlarged image of the gem; imaging means which takes a gem image formed by the enlarging optical system; an image memory which stores a gem image captured from the imaging means; display means which displays at least the gem image; and quality calculation means which calculates at least one piece of quality information out of the polishing state, color hue, clarity, carat, and inclusion state of the gem on the basis of at least one of the position information and the luminance information of the gem image stored in the image memory (Refer to claim 1 of Japanese Patent No. 3392926).
Moreover, there is a gem appraising method including: causing light from a light source to impinge on a gem illumination unit to illuminate a gem arranged inside the gem illumination unit from all angles; capturing image information by imaging the gem from a position opposite to the gem; creating a histogram by measuring a luminance distribution of the gem on the basis of the image information; analyzing a mode value of the histogram and a distribution state to the low luminance side of the mode value; and determining and evaluating the qualities of the shape and the polishing state of the surface of the gem on the basis of the result of analysis (Refer to claim 20 of Japanese Patent No. 3392926).